Model Boat Mayhem
Technical, Techniques, Hints, and Tips => Other Technical Questions... => Topic started by: SteveG17 on February 07, 2022, 01:09:51 am
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Can anyone give me advice about water scoops ?
I'm considering changing the current "pipe" style for one of the flush fitting type. Would there be a massive drop in water flow ? The trade is less drag and a tidier finish.
The boat in question is a Sea Queen, powered by a brushless motor.
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Hullo Steve...
What are you aiming for?
1. increase in cooling capacity?
2. reduction in drag & increase in speed?
3. purely aesthetics?
The black injection molded pickup appears to have a squarish or rectangular mouth, the streamlined [plated brass?] pickup appears to have a round drilled mouth
You could draw a 1/2 section GA of each scoop type, but when it comes down to tin tacks, the aperture available for water to be forced [up] and into the pickup is relative to the internal surface area calculated [this is the surface area in the vertical plane within the scoop at change or direction from the horizontal to the vertical]
So whilst the streamlined version may 'appear' more hydrodynamic........however based upon equal surface areas' I would think any variance in either volume or velocity of water being collected would be 1/2 a dozen zero's after the decimal point O0
A similar thought of equal surface areas' could be applied to an increase in actual drag over a visual profile with those 1/2 a dozen zero's
The one that always gets me is the 'Cd' values [co-efficient of drag] in automobiles ....a sleek Arrow shaped sports car has a Cd of 0.25, then a Boxy SUV, a Cd of 3.2
Derek
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for my model I didnt need cooling water, I just wanted a pickup and a realistic water flow from a stern exhaust tube, I started with a 1/8" brass dome and drilled a 1mm hole through the fitting, then I relieved the front edge of the fitting down to about 1/16" leading to the through hole, this whole was mounted just behind the rudder in the prop wash and after sea trials I widened the hole out to 1.5mm and it now produces a nice stream from the stern, could this be used to cool a motor - certainly, you could increase the flow by opening out the through hull hole, so even the simplest of flush skin fittings can produce an adequate flow of water.
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Hi Grendel,
Thanks for the info, that's all I was needing to hear from someone who had "similar" type of intake.
I somehow didn't think the flush scoops would be produced if they were totally useless !! your homemade approach works, so should be good to go with the type I'm considering installing.
Steve
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Hi Steve, is the brushless motor a out runner or in runner.?and are you cooling the esc as well?
Where were you thinking of fitting the scoop? you may need 1 for the motor and 1 for the esc.
John
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Just how much drag are you trying to reduce? It was noted by Supermarine that flush riveting allowed an increase of 20mph as opposed to round headed rivets, - - - - - but that was on a Spitfire.
Back in the days of IC power, it was necessary to have some form of cooling system. The fitting of choice was the much neater bent brass tube supplied by either RipMax or Keil Kraft. Later, the plastics for everything brigade, much like the superglue fraternity is now, could only come up with the crude monstrosity shown due to the limitations of the material used and the cheapness of tooling to produce it.
In most cases the term 'Scoop' was a misuse as although this effect is now used to create a waterflow. for whatever reason, necessity OR effect, the accepted positioning was immediately behind the prop with the tip of the prop forcing water into the tube. This meant that as soon as the boat was put into the water, the cooling was initiated WITHOUT forward motion, so the term scoop was cobblers.
Back to your original question, if the aerodynamic performance is being compromised, gerrabiggermotor.
Regards Ian.
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heres a few pictures of mine - its really nothing special, yet there is enough flow to produce a 3" jet from the exhaust port. that is enough to lift the water up over an inch and eject with some force after 2 bends in a 3mm brass tube. its probably a couple of inches behind the prop too
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The 'flush type' pickups are for fast / speed boats, unless pump assisted. :-)
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How I do mine
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Thank you all for the advice, it is helping with my decision making.